Test writing has been undertaken in order to record information with a high precision on optical disks. Test writing means actions for seeking the optimum recording parameters in response to the environmental temperature at that time and the characteristics of laser beam transmitted by the drives loaded in order to form good recording marks. Optical disks such as DVD-RW, DVD+RV, BD-RE and the like use materials of a composition called “eutectic system” in their recording film. In the recording devices now being produced, normally for test writing on these optical disks, the recording conditions prewritten in the optical disk are read in the first place, and then the laser power is adjusted. The recording condition referred here, for example, the set value of laser power indicated by the write power level (Pw) of a high laser power, the erasing power level (Pe) of a middle power, a set value of laser power represented by the bias power level (Pb), and the respective pulse width of the first pulse constituting multi pulse wave, a plurality of successive middle pulse and last pulse.
In actual test writing, the method of fixing the ratio between the Pw and the Pe prewritten in the optical disk based on these recording conditions and finding out the optimum recording conditions of the laser power as parameters has been adopted. This method is called “the optimum power control method (OPC).” In relatively low speed recording such as BD1×, DVD-RW2-4× and the like, good recording quality has been obtained by test writing by changing only laser power of such a fixed Pw/Pe ratio.
The research and development efforts are now being made in the high-speed recording and reproduction technology in these optical disks. For example, in Optical Data Storage 2003 and Proceedings of SPIE Vol. 5069 (2003), p 130 (Non-patent Document 1), a recording technology with a recording speed of 216 Mbps corresponding to BD 6× is described. As the recording speed accelerates, write strategy adapted to higher speed, or so-called 2T strategy is now being studied. 2T strategy means a write strategy that equalizes the number of recording pulses of a pair of neighboring marks, one of even number length and the other of odd number length. Specifically, as FIG. 2 shows, for example when the shortest mark length is a 2T mark, the 2T mark and the 3T mark emits a single rectangular pulse, and the 4T mark and the 5T mark emits two pulses, the first pulse and the last pulse. The 6T mark and the 7T mark emit three pulses, a first pulse, a middle pulse and a last pulse.
As an example of this 2T strategy, the Japanese Patent Application Laid Open 1997-134525 (corresponding U.S. Pat. No. 5,732,062, Patent Document 1) describes that, for recording either a mark length from even number length mark or odd number length mark corresponding to the recording channel clock frequency in the multi pulse recording system consisting of the first pulse, a plurality of successive middle pulses and the last pulse, the pulse width of the first pulse and the last pulse is made almost identical with the recording channel clock frequency.
And the Japanese Patent Application Laid Open 1999-175976 (corresponding to U.S. Pat. No. 6,256,277, Patent Document 277) proposes the method of forming a recording wavelength in such a way that the shortest pulse width among the multi pulse may be longer than a half of the window width. This will enable to secure a sufficient cooling time of the recording medium, to reduce the frequency component of the laser driving current and therefore to form marks with a sufficient accuracy during a high-speed transmission.
Furthermore, the Japanese Patent Application Laid Open 2003-30833 (Patent Document 3) as well as the Japanese Patent Application 1999-175976 adopt the method of not only making the frequency of the middle pulse string longer than the recording channel clock frequency but also of changing the edge position of the first pulse and the last pulse depending on the preceding space or the succeeding space. It is stated that the present method enables to restrict to the minimum extent possible edge shift due to heat interference in the track direction involved in the case of recording at a high density and high transmission rate and therefore to control recording at a high precision.
And Japanese Patent Application Laid Open 2001-331936 (corresponding to US 2001/053115A1, Patent Document 4) describes the formation of pulse string by shifting the reference clock depending on the even code train or the odd code train and the formation of the write pulse strategy for even number and odd number by changing the duty ratio for the first pulse and the last pulse respectively in the case of odd number and the case of even number.
Incidentally, with regard to the recording mark shape control effect of the 2T strategy during the high-transmission rate recording is described in details, for example, in Optical Data Storage 2000, and Proceedings of SPIE Vol. 4090 (2000), p 135 (Non-Patent Document 2).    [Patent Document 1] Japanese Patent Application Laid Open 1997-134525    [Patent Document 2] Japanese Patent Application Laid Open 1999-175976    [Patent Document 3] Japanese Patent Application Laid Open 2003-30833    [Patent Document 4] Japanese Patent Application Laid Open 2001-331936    [Non-Patent Document 1] Optical Data Storage 2003, Proceedings of SPIE Vol. 5069 (2003), p 130    [Non-Patent Document 2] Optical Data Storage 2000, Proceedings of SPIE Vol. 4090 (2000), p 135